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(CNN) -- A New York Times reporter was released from jail Thursday afteragreeing to provide evidence to a federal grand jury investigating the leak of a CIA operative's name.

Judith Miller will appear before the grand jury Friday after spending 12 weeks behind bars protecting a confidential source, whom she said has cleared her to testify.

Miller said her attorneys reached an agreement with prosecutors on the scope of her testimony that "satisfied my obligation as a reporter to keep faith with my sources."

"It's good to be free," Miller said in a statement. "I am leaving jail today because my source has now voluntarily and personally released me from my promise of confidentiality regarding our conversations."

She did not identify the source.

New York Times publisher Arthur Sulzberger Jr. said the newspaper supported Miller's decision.

"We are very pleased that she has finally received a direct and uncoerced waiver, by phone and in writing, releasing her from any claim of confidentiality and enabling her to testify," he said in a statement.

Miller was released from a federal facility in Alexandria, Virginia, at about 4 p.m. after a contempt order against her was lifted by a federal judge, a source with detailed knowledge of her case told CNN.

The chain of events that led to the contempt charges against Miller began in July 2003, when syndicated columnist Robert Novak, who is also a CNN contributor, identified Valerie Plame as a CIA operative in his column. He cited unidentified senior administration sources for the information.

Plame's husband is Joseph Wilson, a former U.S. ambassador to Iraq. Wilson charged that his wife's name was leaked to retaliate against him after he disputed Bush administration statements that Iraqi dictator Saddam Hussein had tried to purchase uranium in Africa.

That assertion was used as part of the administration's case for justifying the invasion of Iraq in March 2003.

Because federal law makes it a crime in some cases to deliberately reveal the identity of a CIA operative, the Justice Department launched an investigation, headed by special prosecutor Patrick Fitzgerald, the U.S. attorney in Chicago, Illinois.

Journalists subpoenaed

As part of his probe, Fitzgerald subpoenaed a number of journalists to testify about their sources, including Miller.

Despite the fact that she never actually wrote a story on Plame or Wilson, Miller refused to testify about sources she developed during her research. She was jailed for contempt in July.

She could have been held until October, when the grand jury's term will expire.

New York Times Executive Editor Bill Keller said that until recently, Miller had received "only a generic waiver" of her confidentiality promise, "and she believed she had ample reason to doubt it had been freely given."

"In recent days, several important things have changed that convinced Judy that she was released from her obligation," Keller said in a statement. He did not provide details of what those changes were.

Miller said in her statement that she would not comment further until after she testifies.

Time reporter Matthew Cooper testified in July after the magazine provided investigators with his notes.

Cooper told reporters that Bush's chief political adviser, Karl Rove, told him Wilson's wife worked for the CIA but did not say her name.

Cooper also said that Lewis "Scooter" Libby, chief of staff for Vice President Dick Cheney, confirmed that piece of information.

President Bush told reporters in July that "If someone committed a crime, they will no longer work in my administration."

When asked in June 2004 whether he stood by his promise to fire whoever was found to have leaked Plame's name, Bush replied, "Yes."

Fitzgerald last year also questioned NBC Washington bureau chief Tim Russert, who has said he was not the recipient of a leak concerning Plame's identity.